1. Field of the Invention
The present invention relates to a high frequency circuit device for use in a microwave band, for example, an antenna-sharing device, and to a communication apparatus.
2. Description of the Related Art
High frequency circuit devices having a plurality of high frequency circuits formed on one circuit substrate have been known. One example is an antenna-sharing device in which a transmission filter and a reception filter, which are high frequency circuits, are mounted onto one circuit substrate. In this case, one ground electrode is provided substantially on the whole of the mounting surface (back side) of the circuit substrate excluding the area for a transmission terminal, an antenna terminal, and a reception terminal. This single ground electrode is common to the transmission filter and the reception filter.
Examplary portable telephone systems in which transmission and reception are simultaneously performed are analog systems, CDMA systems, or the like. An antenna-sharing device for use in these systems has a frequency characteristic (hereinafter, referred to as an isolation characteristic) such that a transmission signal is attenuated by a reception filter so that the transmission signal is prevented from strongly affecting a low noise amplifier or the like of a reception system circuit via the reception filter.
However, in the above described antenna-sharing device, the ground electrode is common to the transmission filter and the reception filter. Therefore, there are some cases where the ground current of the transmission filter and that of the reception filter electromagnetically interfere with each other in the ground electrode, and are coupled. When this electromagnetic coupling occurs, the isolation characteristics are deteriorated.
To overcome the above described problems, preferred embodiments of the present invention provide a high frequency circuit device, an antenna-sharing device, and a communication apparatus in which electromagnetic coupling between the ground currents of high frequency circuits can be inhibited.
One preferred embodiment of the present invention provides a high frequency circuit device comprising a plurality of high frequency circuits disposed on a single circuit substrate, ground electrodes of each of the plurality of high frequency circuits being disconnected from each other on the circuit substrate. More concretely, a ground electrode is disposed on the circuit substrate for each of the plurality of high frequency circuits. The ground electrodes are provided with a slit so as to be mutually isolated. As at least one of the plurality of high frequency circuits, for example, a filter comprising a coaxial dielectric resonator, an integrated-type dielectric filter, or a variable-frequency type filter having a voltage-controlled reactance element may be employed.
With above-described configuration, the ground currents of the respective high frequency circuits are inhibited from electromagnetically interfering with each other in the ground electrodes, and thereby, electromagnetic coupling between the ground currents of the high frequency circuits can be prevented.
Preferably, electronic components constituting the high frequency circuits are mounted onto the circuit substrate with a gap being provided between adjacent high frequency circuits, and the position of the slit provided between the ground electrodes overlaps the position of the gap provided between the high frequency circuits. Thereby, electromagnetic coupling of the ground currents, caused when the electronic components constituting the high frequency circuits come into contact with each other, can be prevented, an addition, electromagnetic coupling between the ground currents of the high frequency circuits in the ground electrodes can be prevented.
Also, preferably, shield covers are provided to correspond to each of the plurality of high frequency circuits, and the shield covers are connected to the ground electrodes independently of each other. Thereby, electromagnetic coupling between the ground currents of the high frequency circuits in the ground electrode can be prevented more effectively.
Preferably, in the high frequency circuit device of the present invention, at least two of the high frequency circuits have a common input-output terminal, and the portions in the vicinity of the common input-output terminal of the respective ground electrodes of the two high frequency circuits are electrically connected to each other by an electrically-connecting part.
In the case in which the ground electrodes of the respective plurality of high frequency circuits are disconnected from each other, grounding can be insufficient in some cases, depending on the shape and size of the ground electrode of a printed wiring substrate onto which the high frequency device is mounted, when the high frequency circuit device is built in practice in an electronic device such as a portable telephone or the like. In this case, sufficient grounding can be achieved by making predetermined portions of the plurality of ground electrodes conducting by an electrically-connecting part. Unwanted electromagnetic coupling between the ground currents of the high frequency circuits is substantially negligible, since the conduction is carried out only in a part of each ground electrode.
Further, in an antenna-sharing device and the communication apparatus according to the present invention, each are provided with the high frequency circuit device having the above-described characteristics. Accordingly, electromagnetic coupling between the ground currents of the high frequency circuits can be inhibited, and an excellent isolation characteristic can be attained.
Hereinafter, embodiments of a high frequency circuit device, an antenna-sharing device, and a communication apparatus according to the present invention will be described with reference with the attached drawings.